Have you performed a compression test on all cylinders and that one in particular? This should be your first test.
Since it doesn't appear to be a blown headgasket or cracked head, I'd suspect a broken piston ring(s) or even a hole in the piston top. It could even be a stuck or broken exhaust valve spring or a burned exhaust valve causing the cylinder to have little or no compression.
If you don't have a compression gauge, go to Auto Zone or Advance Auto Parts. Both stores will loan you one for free. (pay the deposit and return the tool when finished for full refund)
Check your oil for coolant and/or gasoline. Gasoline means its getting into the crankcase past the piston. Coolant means there is an internal headgasket leak.
Last edited by Otto Skorzeny; 10/25/2021 4:39 PM.
